Java.lang.Boolean cannot be passed to java.util.LinkedList

Question

I have HashMapwhere the key is of type Stringand the value is of type of LinkedListtype String.

So basically, this is what I'm trying to do.

while (contentItr.hasNext()) {
    String word = (String) contentItr.next();
    if (wordIndex.containsKey(word)) {
        LinkedList temp = (LinkedList) w.get(word); //Error occurs here
        temp.addLast(currentUrl);
    } else {
        w.put(word, new LinkedList().add(currentUrl));
    }
}

The first time I add a key pair, value, I get no error. However, when I try to get the linked list associated with an existing key, I get the following exception:

java.lang.Boolean cannot be cast to java.util.LinkedList. 

I have no way to explain why this exception occurs.

Answer 1

Try this instead:

while (contentItr.hasNext()) {
    String word = (String) contentItr.next();
    if (wordIndex.containsKey(word)) {
        LinkedList temp = (LinkedList) w.get(word);
        temp.addLast(currentUrl);
    } else {
        LinkedList temp = new LinkedList();
        temp.add(currentUrl);
        w.put(word, temp);
    }
}

, , , Map - add , Map. , Map - LinkedList.

, . ( , ), , - :

Map<String, String> wordIndex = new HashMap<String, String>();
Map<String, LinkedList<String>> w = new HashMap<String, LinkedList<String>>();

List<String> content = new ArrayList<String>();
Iterator<String> contentItr = content.iterator();

, , , :

while (contentItr.hasNext()) {
    String word = contentItr.next();
    if (wordIndex.containsKey(word)) {
        LinkedList<String> temp = w.get(word);
        temp.addLast(currentUrl);
    } else {
        LinkedList<String> temp = new LinkedList<String>();
        temp.add(currentUrl);
        w.put(word, temp);
    }
}

- LinkedList ArrayList ( ) LinkedList - , , - addLast ( add), - :

Map<String, String> wordIndex = new HashMap<String, String>();
Map<String, List<String>> w = new HashMap<String, List<String>>();

List<String> content = new ArrayList<String>();
Iterator<String> contentItr = content.iterator();

while (contentItr.hasNext()) {
    String word = contentItr.next();
    if (wordIndex.containsKey(word)) {
        List<String> temp = w.get(word);
        temp.add(currentUrl);
    } else {
        List<String> temp = new ArrayList<String>();
        temp.add(currentUrl);
        w.put(word, temp);
    }
}

Answer 2

List.add boolean, boolean. else LinkedList, (add), boolean .

? w Map<String,List<String>>, . , .